Proper well Plug & Abandonment (P&A) design requires an accurate picture of the current well status, since it represents the starting point to ensure the permanent isolation of zones with potential flow. The greater the amount and quality of data available, the clearer the picture of the well, the better the P&A design. Then, the selection of the most suitable technologies for the specific case allows optimizing the operational sequence thus minimizing the related costs, typically around 50% of the global asset decommissioning cost. Missing or inaccurate data at the P&A design phase results in a conservative approach, due to the many uncertainties regarding the well. Data quantity and, mainly, quality is often dependent upon the age of assets and the existence of a proper Well Data Management System. This paper brings the P&A experience of a platform-based six-well asset in Africa, with no available well data repository resulting in a thorough "hunt for information" to generate a small database and identify the main data gaps relevant to the P&A operation being designed. The collected data, ranging from 10 to 45 years of age, was highly fragmented and heterogeneous. For some wells, the missing information even included well construction files, cement logs, some overburden lithology parameters and, for one of the wells, the characteristics of wellhead and annulus fluid. The execution of an uncertainty analysis based on the good practices applied in the North Sea and the Gulf of Mexico, showed that P&A cost could have varied between M$ 3.7 and 7.5 per well. The latter value was due to additional well barriers resulting from the uncertainty of well status. Analysis of the initial BoD and potential optimization of the P&A sequence resulted in the definition of three scenarios: Best Case (full optimization), Worst Case (no optimization) and Base Case (limited optimization based on gathered information). Two wells are discussed in this paper: Well A, with a moderate level of information, translated into an increase from the Best Case of 18%, representing around M$ 0.7; Well B, with very poor data available, translated into an increase from the Best Case of 75%, of which around 36% or M$ 1.3 related to missing information. As a result, the final P&A scenario led, for the entire asset, to an estimated increase of M$ 6 to 7 vs. the Best-Case scenario. A simple and adequate Well Data Management System, also described in this paper, would have allowed to provide a cost-effective P&A design. The above "M$ 6 to 7" value (around 1 M$ per well) can be considered as a good indication of the value of such a system, although it is conservative in nature, since further benefits could have been also achieved during the production life of the asset.
Among the strategic issues of the Oil & Gas Industry, management of well integrity currently plays a key role, since it allows to simultaneously achieve two major objectives: minimize risk of uncontrolled release of hydrocarbons and extend the life of wells, thus getting the most from reservoirs. Well integrity is about maintaining at least two independent well barriers at all times. This prevents reservoir fluids from being unintentionally and uncontrollably released at surface, and from migrating to other underground layers. However, degradation over time may weaken the elements comprising well barrier envelopes, and therefore impair well integrity if not taken into due consideration. This paper describes an innovative approach to well integrity, which effectively puts the concept of "proactive management" into practice: the aim is not only to ensure that wells operate safely today, but also to be reasonably confident that they will properly work in the future in order to achieve an extended production life and optimize operational expenditures. The subject approach complies with the ISO TS 16530-2 "Well Integrity for the Operational Phase", and uses both a failure mode analysis and a risk assessment technique to estimate the residual well life, on the basis of the expected degradation rate of well barrier elements. The described approach enables to: Evaluate the current well integrity status through a risk-based perspectiveAnticipate future well integrity issuesElaborate a suitable risk reduction action planIdentify proper monitoring and maintenance requirements. A dedicated software has been developed to effectively support the analysis of the current well integrity status and the identification of the well barrier elements that are expected to become critical in the future. The main characteristics of the software are also described.
The ever more challenging environments in which new wells are to be drilled, the uncertainties of the current market, and the availability of effective secondary and tertiary enhanced recovery (EOR) technologies, make the extension of existing wells' life more advisable than drilling new wells. To properly and proactively manage the degradation of Well Barrier Elements (WBEs) over time, thus ensuring the extension of wells life, a specific methodology and software have been developed. The concept of "Wells Life Extension" not only requires to get an adequate knowledge of the current wells integrity status, but also to predict future critical WBE(s) in order to put in place ad-hoc preventive measures. The methodology described in this paper includes three main phases: Well Integrity Assessment, which evaluates today's well integrity status through a risk-based approach.Estimation of Wells Ageing, which estimates the residual well life based on the understanding of WBEs ageing mechanisms.Definition of Intervention Plan Options, in which wells are classified on the basis of specific parameters, and then prioritized for future interventions through a cost-benefit analysis. The implementation of such methodology has allowed Customers to find out the most appropriate actions to be carried out on their ageing wells, with the objective of keeping production performances and safely operating the wells in line with the planned targets. Moreover, it has enabled to properly plan such actions over time, on the basis of the risk levels associated to the failure modes of each WBE, thus preventing and mitigating the need of potentially expensive interventions and protracted downtimes. Furthermore, emergency situations that would even increase costs and/or failures impacts, have been prevented, mitigated, and proper monitoring and maintenance programs have been executed in order to manage risks over time. In summary, the overall benefit of the presented methodology and software consists in anticipating well integrity issues and extending wells life through a proactive and cost-effective approach, that can enhance assets reliability, improve safety levels and minimize both downtimes and costs associated to WBEs failures.
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